The present invention will be described with reference to data traffic management in an asynchronous transfer mode (ATM) network for broadband communications but it is to be understood that the basic concept disclosed is applicable to any data traffic management device which services multiple output ports having different data transmission rates.
Asynchronous transfer mode (ATM) is a networking technology that provides broadband communications and differentiated qualities of service (QoS). The technology, which utilizes a fixed length cell, is well-suited to the transmission of voice, video and data utilizing both real-time and non-real-time service categories. Statistical multiplexing is used in ATM switches to allow for a high efficiency of resource utilization. In order to take advantage of the statistical nature of ATM traffic and still ensure some guaranteed QoS to network data it is important that the streams of ATM data conform to certain specific parameters. These parameters and the guaranteed qualities of service make up the traffic contract as established by the ATM Traffic Management Forum.
In ATM switches it is often useful and/or necessary to shape or schedule ATM cells from various traffic streams. This scheduling ensures that the traffic conforms to the specified parameters for each particular stream which leads to better overall network performance. There are applications where a shaping entity in an ATM system needs to schedule a mixture of traffic which is bound for several output ports. Each of these output ports may have a different data rate parameter. The requirement to service multiple data streams to output ports having different data rates requires or at least implies that the scheduling entity must adopt a different timing reference for each output port.